1. Field of the Invention
The invention relates to polymeric viscosity index (V.I.) improvers--dispersant additives for synthetic and petroleum oils, particularly lubricating oils, methods for their preparation, and oil compositions containing them. These additives comprise a hydrocarbon polymer, for example a copolymer of ethylene with one or more C.sub.3 to C.sub.28 alpha-olefins, preferably propylene, or a hydrogenated copolymer of styrene and butadiene or isoprene, etc., which has been grafted with an acid moiety, e.g. maleic anhydride, followed by reaction with a polyamine, preferably a tertiary polyamine having only a single acetylable amine group, followed by reaction with ammonia or monoamine.
2. Prior Disclosures
Hydrocarbon polymers, particularly ethylenepropylene copolymers, are in widespread use as viscosity index (V.I.) improving additives for oil compositions, particularly lubricating oil compositions. A substantial body of prior art exists directed towards further reacting these ethylene V.I. improvers to form a multi-functional V.I. improver. This is a material useful as a V.I.--dispersant oil additive so as to improve not only the V.I. properties of the oil but to also impart dispersancy so as to suspend sludge that may form during the operation or use of the lubricant and to inhibit varnish deposition in engines. Various patents teach grafting ethylene copolymers with maleic anhydride, followed by reaction with an amine. A number of these prior disclosures teach reducing or avoiding the use of polyamine having two primary amine groups to thereby reduce crosslinking problems which become more of a problem as the number of amine moieties added to the polymer molecule is increased in order to increase dispersancy. Generally, these patents used a primary-tertiary amine.
German Published Application No. P3025274.5 teaches an ethylene copolymer reacted with maleic anhydride in oil using a long chain alkyl hetero or oxygen containing amine.
U.S. Pat. No. 4,132,661 grafts ethylene copolymer, using peroxide and/or air blowing, with maleic anhydride and then reacts with a primary-tertiary diamine.
U.S. Pat. No. 4,160,739 teaches an ethylene copolymer which is grafted, using a free radical technique, with alternating maleic anhydride and a second polymerizable monomer such as methacrylic acid, which materials are reacted with an amine having a single primary, or a single secondary, amine group.
U.S. Pat. No. 4,171,273 reacts an ethylene copolymer with maleic anhydride in the presence of a free radical initiator and then with mixtures of C.sub.4 to C.sub.12 n-alcohol and amine such as N-aminopropylmorpholine or dimethylamino propyl amine to form a V.I.-dispersant-pour depressant additive.
German published application No. 2753569.9 shows an ethylene copolymer reacted with maleic anhydride by a free radical technique and then reacted with an amine having a single primary group.
German published application No. 2845288 grafts maleic anhydride on an ethylene-propylene copolymer by thermal grafting at high temperatures and then reacts with amine having one primary group.
French published application No. 2423530 teaches the thermal reaction of an ethylene copolymer with maleic anhydride at 150.degree. to 210.degree. C. followed by reaction with an amine having one primary or secondary group.
The use of non-ethylene hydrocarbon polymers to form V.I.-dispersant additives is also known in the art such as those of U.S. Pat. Nos. 3,903,003; 4,077,893 and 4,141,847.
Generally speaking, while the use of amines having a single primary group, such as primary-tertiary amines, can reduce cross-linking and gelling, particularly at relatively high levels of maleic anhydride grafting, an undesirable high degree of viscosity increase may still occur. The present invention represents a further improvement over the prior art, wherein this viscosity increase can be further inhibited by treatment with aliphatic monomaines.